[PATCH] block: put the reference of the io scheduler module after switching back

[Jinlong Chen <chenjinlong2016@xxxxxxxxxxx>]

Hi!

Thank you for reviewing!

> 
> I got it now if switch none failed, old queue is not added to the list,
> and later blk_lookup_qe_pair() will fail to lookup the queue.
> 

That's what I'm going to say. :)